1. Field of the Invention
This invention relates generally to semiconductors and fabrication methods therefor, and more particularly, to a semiconductor device having a resin sealing portion and a fabrication method therefor.
2. Description of the Related Art
In recent years, there is a need for reducing the size of semiconductor devices for use in non-volatile memory media or the like of portable electronic devices such as, for example, mobile telephones, and IC memory cards. In order to achieve this need, packages of the semiconductor devices have to be thinner.
Japanese Patent Application Publication No. 8-153832 discloses a technique of forming a resin sealing portion by use of a sheet-shaped resin.
FIG. 1A and FIG. 1B are views illustrating problems posed by the conventional example. Referring to FIG. 1A, semiconductor chips 22 and 24 are stacked and mounted on a wiring substrate 10 of a glass epoxy substrate or the like serving as a chip mounting portion. The semiconductor chips 22 and 24 are electrically coupled to pads 16 of the wiring substrate 10 by means of wires 26 and 28. The semiconductor chips 22 and 24 are resin-sealed by a resin sealing portion 30 of epoxy resin or the like. Land electrodes 12 are provided at a surface of the wiring substrate 10 opposite to another surface on which the semiconductor chips 22 and 24 are mounted, and solder balls 14 are provided at the land electrodes 12. There are also provided in the wiring substrate 10, wires for connecting the pads 16 and coupling portions that couple the pads 16 and the electrodes 12, however, a detailed description will be omitted here.
A distance H between the surface of the semiconductor chip 24 and the top surface of the resin sealing portion 30 is reduced to make the package of the semiconductor device thinner. If so, it will be difficult to fill the resin for sealing between the die that molds the resin sealing portion 30 and the top surface of the semiconductor chip 24 at the time of forming the resin sealing portion 30. This results in the generation of an unfilled portion 90 where the resin is not filled, at the top portion of the semiconductor chip 24. Also, if the distance H is reduced, a filler at the surface of the resin sealing portion 30 will be easily removed, thereby forming a removed portion 91 from which the filler is removed. At the time of printing a mark on the top surface of the resin sealing portion 30, the semiconductor chip 24 will be damaged by laser at the unfilled portion 90 or the removed portion 91. In addition, as indicated by dotted circles 92, the wires 28 may be exposed from the resin sealing portion 30. Therefore, it is difficult to reduce the distance H.
FIG. 1B is a view illustrating the problem of the semiconductor device with the technique disclosed in Japanese Patent Application Publication No. 8-153832. Semiconductor chips 22, 23, and 24 are stacked and mounted on the wiring substrate 10. The semiconductor chips 22, 23, and 24 are sealed by the resin sealing portion 30. Other configurations in FIG. 1B are same as those in FIG. 1A, and a detailed explanation will be omitted here. The resin sealing portion 30 is formed by arranging a sheet-shaped resin on the mold and then providing the semiconductor chips 22, 23, and 24 and the wiring substrate 10 on the sheet-shaped resin. In such case, since the sheet-shaped resin is interposed between the semiconductor chip 24 and the die, no unfilled portion will be generated on the semiconductor chip 24. However, the viscosity of the resin cannot be lowered at the time of forming the resin sealing portion 30 to avoid the exposure of the wire 28. This will produce an unfilled portion 94 where the resin is not filled at a small portion where one semiconductor chip overhangs another, for example, the semiconductor chip 24 overhangs the semiconductor chip 23. Also, the filler has to be additionally provided to the resin sealing portion 30 to maintain the strength of the whole resin sealing portion 30. This cannot prevent the removal of the filler.